We have been studying the molecular control of circadian behavioral rhythms using Drosophila as a model system. Orthologs of genes initially characterized in the fly,have now been linked to the control of rhythmic behavior and physiology in vertebrates, including fish, frogs, mice and humans. Here we propose three classes of interdisciplinary investigations of the Drosophila clock. (1) We will conduct collaborative structural studies that can help us determine how specific regulatory actions, previously recognized genetically and biochemically, are performed by certain domains of the PER protein. Does the structure of PER indicate how it interacts with TIM and DBT? Do such data suggest how TIM suppresses PER's phosphorylation by DBT? Does a putative LOV domain near the N-terminus of PER possess a flavin binding domain? (2) We will generate new mutations for the analysis of vital clock genes by Conditional Protein Splicing. Our studies of hyper- and hypo-morphic mutations of GSK-3, dbt, vri, and Pdp-1 indicate that each is a key component of the Drosophila clock. However, because null mutations of these genes are lethal, it has been difficult to determine their full effects on the clock. We are developing a form of chemical genetics in which small diffusible molecules will reversibly control the presence of each vital protein in living flies. (3) We will produce new microarray and statistical approaches to clarify features of rhythmic genome activity and to determine if flies use a single molecular mechanism to generate all circadian rhythms. To begin to link the clock to specific behavioral and physiological outputs, we will investigate a novel set of genes that are regulated by a paired action of light and the circadian clock.